Core-shell particles have a core of one material and an enclosing shell of another material. The preparation of core-shell particles, especially particles of nanometer scale size, is of increasing importance. For instance, metal/metal oxide core-shell nanoparticles, such as Sn/SnO2, Zn/ZnO and Cu/Cu2O, where the core and the shell originate from the same material, have shown some potential applications in catalytic reactions, gas sensors, and magnetic materials. Particles of these particular metal elements are readily obtained by chemical reduction of their cations from a suitable solvent. The small metal particles were separated from the liquid and subjected to controlled oxidation of the outer layer with air or oxygen to form the metal/metal oxide core shell materials.
Nickel and nickel oxide compositions are important ferromagnetic materials and they are widely used as catalysts in hydrocarbon conversion reactions. However, the synthesis of Ni and Ni/NiO core-shell materials is more of a problem, mainly due to the difficulty in reducing Ni2+ into metallic nickel through a liquid chemical process using common reducing agents. Currently, nanometer size nickel particles are prepared using one of two methods: (1) physical processing, such as pulsed laser ablation, electron-gun evaporation, electrochemical deposition, or metal-organic chemical vapor deposition, or (2) chemical syntheses, such as surfactant-associated micro emulsion techniques or hydrothermal techniques. The chemical synthesis methods can only be practiced using very dilute nickel solutions (Ni2+ concentrations of 2.5 to 45 mmol/L) in the presence of strong reducing agents.
It would be very useful to have a more efficient method of preparing nanometer sized, Ni/NiO core/shell type materials.